�In this photo provided by Universal, Elvis Schmidt (Shawn Hatosy) and Frankie Ballenbacher (Justin Timberlake) discuss what to do with their hostage in "Alpha Dog." (AP Photo/Universal/Darren Michaels)

Like a puppy brought outdoors after being cooped up inside, "Alpha Dog" takes a while to settle down. Writer-director Nick Cassavetes crowds the screen with a confusing number of images, beginning with Bruce Willis -- as the Mafia-connected father of a small-time drug dealer -- being interviewed for a documentary that serves as a film within the film.

Soon afterward, a group of teenage troublemakers are at a club standing under a music video projected larger than life, so you don't know where you're meant to be looking. It takes far longer than necessary to establish who the main characters are and what their relationships are to one another. The whole thing is dizzying, like "Moulin Rouge" without songs and dances extolling love.

Although the mafioso family is given the surname Truelove -- scion Johnny (Emile Hirsch) is a chip off the old block -- there's little love in the deeply disturbing, and often gratuitously violent, "Alpha Dog." But once it finally comes into focus, Cassavetes builds up a gut-wrenching suspense likely to keep you on the rim of your seat.

Driving through a well-to-do neighborhood in the San Gabriel Valley -- in cruel morning light, it appears as a vast wasteland -- Johnny and his minions spot the 15-year-old half brother, Zack (Anton Yelchin), of a double-crosser named Jake (Ben Foster) who reneged on a loan and, as a further sign of his contempt, defecated on Johnny's carpet. In the wrong place at the wrong time, Zack has just escaped out his bedroom window to avoid a fight with his adoring, but suffocating, mother (Sharon Stone).

Like a gang that can't shoot straight, the young hoods haphazardly kidnap him as revenge without any sense of the enormity of what they've done. Overprotected, Zack sees the whole thing as a lark, a chance to spread his wings -- which he does with two pretty groupies who make themselves sexually available.

Cassavetes has inherited from his late father, the pioneering independent filmmaker John Cassavetes, a way with actors, and he coaxes powerful performances from his young cast, particularly Justin Timberlake as Frankie, a thug with a conscience. When Zack is put in his charge, he develops an affection for the boy and becomes his unlikely protector.

The hugely popular singer shows that he can act with the same contagious energy he brings to his music. A costume designer had an inspired idea to put him in a straw hat, so Frankie immediately stands out in the gang. Timberlake plays him as a bundle of anxiety. He never stands still, appearing at times to break into a jig. You can't take your eyes off him. It's a breakthrough performance on par with Edward Norton's in "Primal Fear."

Hirsch brings the right degree of bluster to Johnny, and Yelchin projects an innocence that will break your heart. Stone also is extremely moving, proving again how hypnotic she can be, given proper direction.

Cassavetes based his script on actual events in the late 1990s. To emphasize "Alpha Dog's" veracity, he flashes dates and times on the screen (9:06 a.m., 10:17 a.m. -- they look like golf start times) and gives each of the 30 or so people who encounter Zack with his abductors a witness number. Instead of intensifying concern over the boy's fate, all these numerals are a distraction.

As uneven as the film is, those with strong stomachs will find it worth sticking with. It's "Justified," if for no other reason than the chance to watch a movie star be born.